Hey
You say you did'nt even feel scared about the idea of doing anything bad, but it obviously did scare you... you would'nt be so distressed and posting here about it if it did'nt, or have this need to confess to your therapist. Think about it.
You've done nothing wrong, and you have't/would'nt of hurt that little boy. Its only OCD that injects this extreme doubt. Your "what if?" is your OCD at work. What if I have HIV? What if I'm going crazy? What if I hurt or would hurt that person? People with OCD are the same, no matter what it is they are obsessing about.
Our obsessions can become disturbingly "real" in our heads, and our patterns of thought and logic very distorted as a result. I know, I have been there, especially when it comes to this obsession that we might somehow cause harm to others. And a lot of people with OCD do feel guilty, when we really have nothing to feel guilty about. Remember that OCD is all about the things you really dont want to happen.
You have'nt lost control at all, and your therapist is not gonna throw you in jail if you tell her of this.

The only thing that I believe is out of control here is anxiety, and that is no fault of your own. It also does not make you crazy. I would say try not to worry, but I know that is a cross we have to bear a lot of the time.
Steve